<template>
<scroll class="listview" :data="data" ref="listview" :listenScroll="listenScroll" @scroll="scroll" :probeType="probeType">
  <ul>
    <li v-for="group in data" class="list-group" ref="listGroup">
      <h2 class="list-group-title">{{group.title}}</h2>
      <ul>
        <li v-for="item in group.items" class="list-group-item" @click="selectItem(item)">
          <img v-lazy="item.avatar" alt="" class="avatar">
          <span class="name">{{item.name}}</span>
        </li>
      </ul>
    </li>
  </ul>
  <div class="list-shortcut" @touchstart="onShortcutTouchStart" @touchmove.stop.prevent="onShortcutTouchMove">
    <ul>
      <li v-for="(item,index) in shortcutList" class="item" :data-index="index" :class="{'current': currentIndex===index}">{{item}}</li>
    </ul>
  </div>
  <div class="list-fixed" v-show="fixedTitle" ref="fixed">
    <h1 class="fixed-title">{{fixedTitle}}</h1>
  </div>
</scroll>
</template>

<script type="text/ecmascript-6">
  import Scroll from 'base/scroll/scroll'
  import {getData} from 'common/js/dom'

  const ANCHOR_HEIGHT = 18
  const TITLE_HEIGHT = 30

  export default {
    created() {
      this.touch = {}
      this.listenScroll = true
      this.listHeight = []
      this.probeType = 3
    },
    data() {
      return {
         scrollY: -1,
         currentIndex: 0,
         diff: -1
      }
    },
    props: {
      data: {
        type: Array,
        default: []
      }
    },
    computed: {
      shortcutList() {
        return this.data.map((group) => {
          return group.title.substr(0,1)
        })
      },
      fixedTitle() {
        if (this.scrollY > 0) {
          return ''
        }
        return this.data[this.currentIndex] ? this.data[this.currentIndex].title : ''
      }
    }, 
    methods: {
      selectItem(item) {
        this.$emit('select', item)
      },
      onShortcutTouchStart(e) {
        let anchorIndex = getData(e.target, 'index')
        let firstTouch = e.touches[0]
        this.touch.y1 = firstTouch.pageY
        this.touch.anchorIndex = anchorIndex
        this._scrollTo(anchorIndex)
      },
      onShortcutTouchMove(e) {
        let firstTouch = e.touches[0]
        this.touch.y2 = firstTouch.pageY
        let delta = (this.touch.y2 - this.touch.y1) / ANCHOR_HEIGHT | 0
        let anchorIndex = parseInt(this.touch.anchorIndex) + delta
        console.log(anchorIndex)
        this._scrollTo(anchorIndex)
      },
      refresh() {
        this.$refs.listview.refresh()
      },
      scroll(pos) {
        this.scrollY = pos.y
      },
      _scrollTo(index) {
         if (!index && index !==0) {
           return
         }
         if (index < 0) {
           index = 0
         } else if (index > this.listHeight.length -2) {
           index = this.listHeight.length -2
         }
         this.scrollY = -this.listHeight[index]
         this.$refs.listview.scrollToElement(this.$refs.listGroup[index], 0)
      },
      _calculateHeight() {
        this.listHeight = []
        const list = this.$refs.listGroup
        let height = 0
        this.listHeight.push(height)
        for(let i=0;i< list.length;i++){
          let item = list[i]
          height += item.clientHeight
          this.listHeight.push(height)
        }
      }
    },
    watch: {
      data() {
        setTimeout(()=> {
          this._calculateHeight()
        }, 20)
      },
      scrollY(newY) {
        const listHeight = this.listHeight
        // 当滚动到顶部 newY>0
        if (newY > 0) {
          this.currentIndex = 0
          return
        }

        //在中间部分滚动
        for (let i=0; i < listHeight.length -1; i++) {
          let height1 = listHeight[i]
          let height2 = listHeight[i+1]
          if (-newY>=height1 && -newY< height2) {
            this.currentIndex = i
            this.diff = height2 + newY
            return
          }
        }
        // 滚动到底部且-newY大于最后一个元素的上限
        this.currentIndex = listHeight.length - 2 
      },
      diff(newVal) {
        let fixedTop = (newVal>0 && newVal < TITLE_HEIGHT) ? newVal - TITLE_HEIGHT : 0
        if (this.fixedTop === fixedTop) {
           return 
        }
        this.fixedTop = fixedTop
        this.$refs.fixed.style.transform = `translate3d(0,${fixedTop}px,0)`
      }
    },
    components: {
       Scroll
    }
  }

</script>

<style scoped lang="stylus" rel="stylesheet/stylus">
  @import "~common/stylus/variable"

  .listview
    position: relative
    width: 100%
    height: 100%
    overflow: hidden
    background: $color-background
    .list-group
      padding-bottom: 30px
      .list-group-title
        height: 30px
        line-height: 30px
        padding-left: 20px
        font-size: $font-size-small
        color: $color-text-l
        background: $color-highlight-background
      .list-group-item
        display: flex
        align-items: center
        padding: 20px 0 0 30px
        .avatar
          width: 50px
          height: 50px
          border-radius: 50%
        .name
          margin-left: 20px
          color: $color-text-l
          font-size: $font-size-medium
    .list-shortcut
      position: absolute
      z-index: 30
      right: 0
      top: 50%
      transform: translateY(-50%)
      width: 20px
      padding: 20px 0
      border-radius: 10px
      text-align: center
      background: $color-background-d
      font-family: Helvetica
      .item
        padding: 3px
        line-height: 1
        color: $color-text-l
        font-size: $font-size-small
        &.current
          color: $color-theme
    .list-fixed
      position: absolute
      top: 0
      left: 0
      width: 100%
      .fixed-title
        height: 30px
        line-height: 30px
        padding-left: 20px
        font-size: $font-size-small
        color: $color-text-l
        background: $color-highlight-background
    .loading-container
      position: absolute
      width: 100%
      top: 50%
      transform: translateY(-50%)
</style>
